The present disclosure is related to oilfield downhole tools and, more particularly, to drilling turbines used for drilling wellbores and generating electrical power.
Drilling of oil and gas wells typically involves the use of several different measurement and telemetry systems to provide data regarding the subsurface formation penetrated by a borehole, and data regarding the state of various drilling mechanics during the drilling process. In measurement-while-drilling (MWD) tools, for example, data is acquired using various sensors located in the drill string as near to the drill bit as is feasible. This data is either stored in downhole memory or transmitted to the surface using assorted telemetry means, such as mud pulse or electromagnetic telemetry devices.
The sensors used while drilling require electrical power and, since it is not feasible to run an electric power supply cable from the surface through the drill string to the sensors, the electrical power must be obtained downhole. In some cases, the sensors may be powered using batteries installed in the drill string at or near the location of the sensors. Such batteries, however, have a finite life and complicate the design of the drill string by requiring a sub/housing that houses the batteries and associated sensor boards. Moreover, batteries take up a substantial amount of space in the drill string and can therefore introduce unwanted flow restrictions for circulating drilling fluid.
In other cases, the sensors may be powered using an electrical power generator included as a separate component in the drill string. For instance, a typical drilling fluid flow-based electromagnetic induction power generator employs multiple rotors coupled to a rotatable shaft and having impeller blades that extend radially therefrom. The impeller blades are placed in the path of a high-pressure flow of drilling fluid derived from the drill string and convert the hydraulic energy of the drilling fluid into rotation of the rotatable shaft. As the rotatable shaft rotates, electrical power is generated in an associated coil generator. Similar to the use of batteries, however, conventional downhole electric power generators require a separate sub/housing that houses the components of the power generator. Moreover, conventional electrical power generators that are separate components typically require the transfer of generated electrical power across separate drilling components or devices, some of which may be rotating at different speeds.